We are interested in specific cell cohesion and in specific adhesion of cells to extracellular materials. We propose to study the molecular basis of these cellular associations and their role in embryonic development. We have evidence that at least two lectins (i.e. carbohydrate binding proteins that can be assayed as agglutinins of appropriate test cells) change strikingly with development of both cellular slime molds and embryonic chick tissues (including muscle, heart, brain and liver). In the slime molds we and others have provided evidence that the lectins, which are detectable on the cell surface, play a role in cell cohesion. The function of the lectins in developing chick tissues is not presently known. We propose to continue to evaluate the role of these lectins in development. Our general approach is: 1) identify and purify lectins from developing tissues: 2) raise antibodies to these purified proteins and use the antibodies for histological localization and, in univalent form, as a reagent for interference with cell interaction; 3) identify the complex saccharides in tissues (e.g. glycolipids, glycosaminoglycans) with which the lectins interact.